Gene Therapy May Help Against Rare Blinding Disease

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The first signs tend to be seen in boys in late childhood, with the disease slowly progressing until vision is lost. There is currently no cure.

MacLaren and his colleagues engineered a virus that would infect the patient's retina but, instead of spreading disease, would instead release a DNA payload that would replace the defective gene with a working copy of the gene.

The phase 1 clinical trial involved six patients aged 35 to 63 -- two with excellent vision, two with good vision and two with damaged vision, according to the case report. In an operation similar to cataract surgery, doctors surgically detached the patients' retinas and then injected the virus underneath using a very fine needle.

Six months after the operation, patients with good or excellent vision retained that vision but could see more in the dark when tested. Loss of night vision is an early sign of the disease, MacLaren said.

The two patients with bad vision experienced improvement, and were now able to read two and four more lines on a sight chart.

Those improvements have lasted for two years in one patient and one year in the other, researchers reported.

"It's too early to say the degeneration has stopped, but the vision we've seen in these two patients has been sustained at one year and two years," MacLaren said in an interview.

Fromer said that the most promising part about gene therapy for eye diseases is that vision loss often occurs very slowly. That means that doctors would have ample time to halt vision loss using a genetic cure.

"You have a lot of time to get that virus into the eye, to correct the defective gene," Fromer said. "The window is large."

MacLaren said this research has focused on choroideremia because it is a relatively simple disease caused by just one defective gene.

By proving this type of treatment can work, he added, doctors can then investigate using it to treat more complicated genetic eye disorders in which multiple genes are malfunctioning.

"This is effectively the first flight across the Atlantic," MacLaren said. "It's one disease, it's quite rare, but it represents a big step forward."